A voluminous cache of secret documents is leaked, shedding new light on official statements and drawing into question some of the rationale for America's involvement in a murky, distant and long-running war.

That would accurately describe the publication in 1971 of the Pentagon Papers, the Defense Department's secret history of the Vietnam War that revealed a "credibility gap" between the Johnson administration's public statements and its private actions.

It might also describe the leak Sunday of thousands of official military documents characterizing the U.S. military's prosecution of the war in Afghanistan.

In the wake of the release of the Afghan documents, the link between the two leaks 39 years apart was made by Julian Assange, the Australian who is the key proprietor of WikiLeaks, the whistleblower Web site that posted the documents and orchestrated their simultaneous publication by the New York Times, the Guardian newspaper of Great Britain and Der Spiegel magazine of Germany. It also was made by Daniel Ellsberg, the renegade Rand Corp. researcher who leaked the Pentagon Papers, first to the New York Times and later to The Washington Post and other newspapers.

"The parallels are very strong," Ellsberg said in an interview Monday. "This is the largest unauthorized disclosure since the Pentagon Papers. In actual scale, it is much larger, and thanks to the Internet, it has moved [around the world] much faster."

Superficially, the two episodes do seem related. In substance, however, the case may be weaker.

Both certainly portrayed their wars in much grimmer terms than those in power would publicly acknowledge. The Pentagon Papers were quickly seized on by those who questioned and opposed the war; a similar fate seems likely for the Afghan archive.

But there are important differences. The key one is the nature of the documents and the substance of what they reveal. The Pentagon Papers were a complete, three-volume history of the war, a 7,000-page narrative spanning a 22-year period. They relied on some of the highest-level documentation possible: White House memos, military reports, CIA and State Department cables. They disclosed official secrets, such as the covert bombing of Laos and Cambodia, and outright lies, such as Lyndon Johnson's plans to widen the war in 1964 despite an explicit campaign pledge to the contrary.

By contrast, the Afghan documents -- more than 91,000 in all -- are a loosely related collection of material covering nearly six years (early 2004 through late 2009) that leaves out important context. Many of the documents are unedited, firsthand reports by military officials, some of which are routine after-action summaries. What's revealing about the material may be what's missing: classified documents that could shed further light on some of the incidents described in the raw material.

"We . . . need to be a little bit sophisticated about the nature of documents," says Steven Aftergood, director of the Federation of American Scientists' Project on Government Secrecy. "The fact that something is written down and even classified does not make it necessarily interesting or true. Documents can mislead as well as inform. The idea that this disclosure constitutes the true record, as opposed to everything we've learned up to now, is naive and ridiculous. These documents are one more collection of data points from which we have to assemble an understanding of what has gone on."

A further distinction: No single message has emerged from the Afghan documents the way it did from the Pentagon Papers.

On Monday, the New York Times emphasized the duplicity of the Pakistan military and secret service and its involvement with the Taliban; the Guardian focused on reports of civilian atrocities; and Der Spiegel underscored how the German government has mischaracterized the military situation in northern Afghanistan that involves German troops. The headlines from the publication of the Pentagon Papers were more consistent: The administration had deceived the public about the war.